Analog to digital converters (ADCs) are used to convert a continuous analog signal to a discrete digital signal. For example, an ADC can convert an analog voltage signal to a digital signal based on samples of the voltage of the analog signal. These samples represent the amplitude of the voltage of the analog signal at different times.
Because of physical limitations, ADCs do not operate perfectly. Thus, the output of an ADC deviates from an ideal value. For example, an ADC can introduce noise into the digital signal it produces. For example, jitter in an ADC can be caused by small timing errors made during sampling of the analog signal. A signal-to-noise (SNR) ratio of the ADC can characterize the amount of noise introduced. An ADC can also be bandwidth limited (i.e., it may only support a specific range of frequencies).
ADCs can be calibrated to evaluate and enhance their effectiveness. For example, the output of an ADC can be tested and evaluated to determine how much this output deviates from an ideal value that would normally be produced if the ADC operated perfectly without introducing any additional noise or error. The ADC can then be adjusted to mitigate the error introduced by the ADC.
Different calibration techniques can be used to evaluate the effectiveness of an ADC. However, each of these techniques has limitations. For example, blind calibration of timing and gain mismatches of ADCs relies on the use of signal statistics such as power spectra, correlation between lanes, etc. One problem with a blind calibration approach is that no single metric works for all possible applications. Calibration approaches that assume that the input signal is band-limited can work well when raised cosine transmission filtering is present but can fail for implementations that do not have this filtering. Correlation schemes work well when the input is sampled at the baud rate but fail for oversampled ADC applications. Further, these typical calibration implementations rely on dedicated hardware (i.e. correlators and filters) to perform ADC calibration.
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